commit 49bac845bf574eb813ea017d9690bc11124c5b88
author Mathieu Chartier <mathieuc@google.com> Tue Jun 27 14:04:41 2017 -0700
committer Mathieu Chartier <mathieuc@google.com> Wed Jun 28 20:15:32 2017 +0000
tree 540dcfbfa3cf2ac2b300c1806d74b49d957d3be9
parent 975bf2ce68e8351e84c618678c4098052514b4e1

Protect cleared regions

Prevent allowing threads seeing references to cleared regions.
This accomplished by using mprotect.

Also refactored some of the code.

Bug: 37187694
Test: test-art-host
Change-Id: I3bdcd08877835962780d55c9c2c521ccda8bc055

runtime/gc/space/region_space.cc

diff --git a/runtime/gc/space/region_space.cc b/runtime/gc/space/region_space.cc
index dba252d..26b7282 100644
--- a/runtime/gc/space/region_space.cc
+++ b/runtime/gc/space/region_space.cc
@@ -29,6 +29,9 @@
 // value of the region size, evaculate the region.
 static constexpr uint kEvaculateLivePercentThreshold = 75U;
 
+// If we protect the cleared regions.
+static constexpr bool kProtectClearedRegions = true;
+
 MemMap* RegionSpace::CreateMemMap(const std::string& name, size_t capacity,
                                   uint8_t* requested_begin) {
   CHECK_ALIGNED(capacity, kRegionSize);
@@ -546,6 +549,9 @@
   if (zero_and_release_pages) {
     ZeroAndReleasePages(begin_, end_ - begin_);
   }
+  if (kProtectClearedRegions) {
+    mprotect(begin_, end_ - begin_, PROT_NONE);
+  }
   is_newly_allocated_ = false;
   is_a_tlab_ = false;
   thread_ = nullptr;
@@ -575,6 +581,9 @@
   alloc_time_ = alloc_time;
   region_space->AdjustNonFreeRegionLimit(idx_);
   type_ = RegionType::kRegionTypeToSpace;
+  if (kProtectClearedRegions) {
+    mprotect(Begin(), kRegionSize, PROT_READ | PROT_WRITE);
+  }
 }
 
 void RegionSpace::Region::Unfree(RegionSpace* region_space, uint32_t alloc_time) {